Earlier studies [9,79–81], using bladder cancer lines and mouse xenograft models for bladder cancer and demonstrating E2-induced proliferation of ERα-positive cells and its inhibition by selective ER modulators, as well as inhibition of the growth of ERα-negative/ERβ-positive tumor by tamoxifen, indicated the stimulatory effects of estrogen on the progression of urothelial cancer. The gene discussed is ESR1; the disease is urinary bladder cancer.